Control by capacitor discharge blocking



July 25, 1950 s. c. ROCKAFELLOW 2,516,422

CONTROL BY CAPACITOR DISCHARGE BLOCKING Filed June 29, 1949 5 TUAR T C. POCKA FELLOW INVENTOR Patented July 25, 1950 CONTROL BY CAPACITOR DISCHARGE BLOCKING '7 Stuart C. Rockafellow, Farming-ton, Mich., as-

signor to Robotron Corporation, Detroit, Mich., a corporation of Michigan Application June 29, 1949, Serial No. 102,085

6 Claims. (Cl. 315-272) I This invention relates to control apparatus and particularly a type thereof wherein the timing period is always started at the same point on an alternating current supply wave.

In many industrial applications for timingand control equipment, it is desirable that the accuracy be held within such limits that a single half cycle from the usual GO-cycle alternating current represents a material interval of time.

In the timing devicesknown prior hereto it has been common to employ as the time determining element a capacitor which is alternately charged and discharged and the time required for discharge to some predetermined level determines the time during which a particular conwhen the current flows in the reverse direction.

Thus, wherever initiation of timing portion of the sequence occurs without regard to the portion of the current cycle in which such initiation is effected, there is a variable element in the time that will be required for the capacitor to discharge since the capacitor sometime will, and

other times will not, have had a slight degree of discharge prior to such initiation Therefore, it is desirable that a timing and control device be provided which will always initiate the timing ular point of the wave-form. Therefore, highly accurate and useful service will be provided by a device which will both eliminate errors due to starting the timing sequence at different points on the wave-form and will also start the flow of current at a preselected point on the waveform, which point may or may not be the same as the point at which the sequence is started.

Accordingly. a principal object of the invention is the provision of an improved timing and control apparatus wherein an electroresponsive device (relay) is supplied with current through an electronic discharge device for a very accurately predetermined period of time.

A further object of this invention is, first, to provide a timing capacitor discharge network, which when charged, will render a control discharge device nonconductive and, second, to control the start of the discharge of the timing 53.5 ment of a flow of current be effected at a partic- '2 capacitor in such a manner that it occurs only at the zero point of the alternating current supply source wave. In this manner the timing of said capacitor will always start at the same point with a result of extreme accuracy in the time of discharge. 7

A further object of theinvention is to provide a timing means as aforesaid having means by which theflow of current may be started at a predeterminable point on the wave-form, which point may or may not as desired be the same point on the wave-form atwhich the timing sequence is started.

A further object is to provide such a device which is simple to construct and will be sturdy and reliable in operation. I I

This invention will be better understood from the following description when considered in connection with the accompanying drawings and its scope will be covered in the appended claims.

Figure 1 is a circuit diagram illustrating an embodiment of my invention.

Figure 2 illustrates the wave form of the supply voltage.

In meeting the objects and purposes enumerated foregoing, as well as other objects and purposes related thereto, I have provided a device having an electric valve in series with the coil of a relay and means holding said valve blocked so long as current is flowing through a second electric valve. Other means including a switch are then provided for blocking said second valve whereby to permit current to flow through the first valve, and holding said second valv blocked for the time required to discharge a capacitor, actuation of said other means being initiable only after the first reversal of current following the closing of said switch. Means are also provided by which the original blocking of said firstnamed valve may be maintained for a predetermined interval of time following the blocking of said second valve in order that the actual flow of current may be caused to start a predeterminable time following'said reversal of current.

Considering now in detail the construction of my device, the transformer Iv has its primary? connected to any convenient alternating current source and has a, plurality of secondary windings.

tive potential on the grid of discharge device l when the anode of said discharge device is positive thus rendering the discharge device nonconductive when the switch 9 is closed, Resistor 8 provides a return path to the cathode of discharge device Ill from its grid. Resistor II provides a load for discharge device'l 0.

The variable resistor 13 and the capacitor I2 form a condenser discharge rate circuit and the resistor I4 is a current limiting resistor to the grid of discharge device 3i. Resistor l5 and capacitor l6 are in the anode circuit of discharge device 3| which, when conducting, places a negative charge on the 'grid of discharge device 3t rendering it nonconductive. Relay H has contacts it to control an external circuit when energized.

In the light of the foregoing, it will be understood that the switch 9 may be any form-oi circuit making device, either mechanical or electrical. and may include, for example, any form of electric 'valve.

Discharge devices Ill, 3| and 30 are of the gas filled type commonly called thyratrons. These discharge devices-have the characteristic of having a grid which controls only the start'of conduction. Once conduction starts, the grid has no more efiect on the conduction and the current "flow stops only when the anode supply reaches ne'ar-ly zero potential. a

The waveform shown in Figure 2 is that of the alternating current wave as supplied from winding 3, the positive portions being indicated at 23 and 22 and the-negative portions being indicated at-2| and 23. Portions-20 and 22 act as a positive supply to the anodes of discharge devices Ill and "SI while portions 2i and 23 act as apositive supply 'to the anode of discharge device 3|]. With an alternating current flowing through to the primary 2'0f the supply transformer I, all filaments are heated and a supply voltage is available from winding 3. At this point, the discharge device 1'0 isconducting because its grid is-tied to its cathode through the resistor 8, and by conducting it is causing a voltage drop across the resistor H. The voltage drop across the resistor H has a polarity of positive-at the-cathodeendwhich'puts a-positivepotential on the grid of the-discharge device 3i, which as it draws currentwill charge capacitor [2 to a negative'potential at the'grid end. Discharge device 3| is conducting which causesa current flow through resistor I5 causing a voltagedrop acrosssaid resistor which charges capacitor It to a negative potential at the anode side corresponding to said voltage drop. This negative potential is placed on the grid of discharge device 30 rendering it nonconductive.

When the initiating switch 9 is closed, negative bias is placed on the grid of discharge device [0 which renders it nonconductive. As

discharge device Ill-is now nonconductive there is no longer a voltage drop across resistor I I, thus the positive potential used to charge capacitor [2, through rid conduction of discharge device 3|, is

removed and capacitor I ZimmediateIypIaceS a negative bias on the grid of discharge device 3| rendering it nonconductive.

govern the time that relay ll remains energized.

The primary purpose of the discharge device It is to provide extreme accuracy in timing. Re-

gardless of when the initiating switch 9 is closed,

the capacitor l2 will always start discharging at point 21 on the A. C. supply wave in Figure 2. If the initiating switch is closed at point 25 or '26 at which time in Figure 2 the discharge device Ifi has already started to conduct, said discharge device li] will continue to conduct since its characteristics, above mentioned, are such that once it has started to conduct it cannot be rendered nonconductive byplacing a negative potential on the grid until the anode supply reaches nearly' z'ero voltage.

Capacitor 52 receives its charging voltagefrom -the positive portions 20 and 22 of A. C. wave in Figure 2. Thus, by controlling the start of discharge -at a definite point on the supply wave, extreme accuracy in timing may be obtained. Regardless of when the initiatingswitch 9 is closed, at points '25, 26, 21, 28 or 29, or elsewhere, the'capacito'r l2 will always start to dischargea't point 21 ori-the curve in Figure 2.

The valuesof capacitor l6 and resistor 15 can also beselected to control the discharge of capacitor lfiso that its potential will always decrease at a single, predetermined, rate which will allow the discharge device 30 to fire at a predetermined time following the point 2'1. This causes the discharge device 30 always to start conducting at the same point in the wave, thus energizing relay l1 at the same time with respect to the A. C. supply wave each time the initiatin switch is closed. Thus, the firing of the discharge device "30does not necessarily occur immediately upon the closing of the switch 9, but rather is subject to two possible delays. First, the discharge device I 0 will not cease to conduct until the wave form reaches the point 21 of Figure 2, namely, until the current reverses its direction. Second, even after'discharge device it) ceases to conduct and causes discharge device 3! similarly and instantly to cease to conduct, discharge device 30' will "not commerce conducting until the capacitor lfihas drained bya' predeterminable amount. The time that discharge device 30 continues to conduct is dependent upon the time that discharge device 31 remains nonconductive, and this depends upon the time required by capacitor [2 to drain to a predetermined level. When this latter occurs, the sequence is completed and the circuit reassumes its initial condition. Therefore, it will be understood that the time that discharge-device 30 conducts is measured by the difierence in'time required'to drain said two capacitors with'ca- 'pacitor l6 draining in the shorter length of time.

of operation that after discharge has been initi-T ated and so long as a potentialcontinues to exist between the principal electrodes the control electrode has no effect upon such discharge; a first resistance and a conductor connecting one end of said resistance to the cathode of said first electrical discharge device and other conductors connecting the anode of said electrical discharge device and the other end of said first resistance, respectively to each side of said source; means including a switch controllable applying a negative bias to the control electrode of said first discharge device; a second resistance and a conductor connecting one end of said resistance to the anode of said second electrical discharge device and the other end of said second resistance, respectively, to each side of said source, the cathode of said second electrical discharge device being connected to the same side of said source as is said other end of said first resistance; a capacitor and resistance in parallel and means connecting one end thereof between said first resistance and said first discharge device and connecting the other end to the control electrode of said second discharge device; circuit means energized from said source and including in series said load means connected to the principal electrodes of said third discharge device and connected thereto in opposite polarity from said first and second discharge devices; a capacitor in parallel with said second resistance and a conmotion from a point between said capacitor and the anode of second discharge device to the control electrode of said third discharge device;

whereby when said switch is open said third dis- I 4 charge device will be non-conductive and when said switch is closed said third discharge device will become conductive only upon the elapsing of a predetermined period of time after the occurrence oi the first reversal of potential following the closing of said switch,

2. In time delay control device for passing current through a load means for a precisely controllable period or time, the combination comprising: a source of alternating potential and a pair of bus conductors energized thereby; first, second and third electric discharge devices, each having a pair of principal. electrodes, a control electrode and at least the first thereof being of such characteristics of operation that after discharge has been initiated and so long as a potential continues to exist between the principal electrodes the control electrode has no effect upon such discharge; a first resistance and means con necting same in series with the principal electrodes of said first electrical discharge device on the cathode side thereof and between said bus conductors; means including a switch controllable applying a negative bias to the control electrode of said first discharge device; a second resistance and means connecting same in series with the principal electrodes of said second electrical discharge device on the anode side thereof and between said bus conductors, said first and second electric discharge device being connected to said bus conductors in the same polarity; a capacitor and resistance in parallel and means connecting one end thereof between said first resistance and first discharge device and connecting the other end to the control electrode of said second discharge device; circuit means energized from said source and including in series said load means connected to the principal electrodes of said third discharge device and connected thereto in opposite polarity from said first and All second discharge devices; a connection from a point between said second resistance and the principal electrode of said second discharge device which is connected thereto to the control electrode of said third discharge device; whereby when said switch is open said third discharge device will be non-conductive and when said switch is closed said third discharge device will become conductive only after the occurrence of the first reversal of potential following the closing of said switch.

3. In a time delay control device for controlling the passage of a current through a load for a precisely controllable period of time, and including a plurality of electric discharge devices each having an anode, a cathode and a control electrode, the combination comprising: a source of alternating potential; a circuit energized there from including a first electric discharge device and a first resistance in series; an independently energized circuit, including a switch, connected to the control electrode in said first electric discharge device; a second circuit including a second resistance and a second electric discharge device in series and means connecting same to said source, the first and second electric discharge devices being connected to said source in the same polarity but said first resistance being in the cathode circuit of said first electric discharge device and said second resistance being in the anode circuit of said second electric discharge device; a circuit including a capacitor and a resistor in parallel connecting the control electrode of said second electric discharge device to the cathode of said first electric discharge device; a third electric discharge device and means connecting same and said load in series with each other and with said source; said load being in the anode circuit of said third electric discharge device and said third electric discharge device being connected to said source in opposite polarity to that of said first and second electric discharge device; a capacitor and means connecting it in parallel with said second resistance; means connecting the control electrode of said third electric discharge device to the anode of said second electric discharge device; the last named capacitor and second resistor being so related to each other as to require a less time to discharge said capacitor through said resistor than the time required to discharge the capacitor through the resistor in the control electrode circuit of said second discharge device; and each of said electric discharge devices being of such characteristics that when a current passage is started therethrough a subsequent energizing of the control electrode will not eiiect such passage whereby closing of said switch will effect current passage through said load after a predetermined period of time following the first reversal of said alternating potential subsequent to said closing of said switch, and said current will continue to flow through said load for a precisely predeterminable time and then automatically terminate and the opening of said switch will permit said capacitors to become again charged in preparation for repeating the cycle.

4. In a time delay control device for controlling the passage of a current through a load for a precisely controllable period of time, and including a plurality of electrical discharge devices each having an anode, a cathode and a control electrode, the combination comprising: a source of alternating potential; a circuit energized therefrom including a first resistance; means congamma a capacitor and a'resistor in parallel connecting thecontr'ol electrode of said electric discharge device to that end of said first resistance which is connected to the same side of said source as is the anode of said electric discharge device; anotherele'ctri'c discharge device and means connecting same and'said load in series with each other and with said source; said load being in the anode circuit-of said last-named electric discharge device and the last-named electric discharge device being connected to said source in opposite polarity to that of-said first-named elec- -'tric-discharge device; a capacitor and-meansconnecting same in parallel with said second resistor; a circuit connecting the control electrode of said last-named electric discharge device to the anode of said first-named electric discharge device; the last-named capacitor and second resistor being so related to each other as to require a less time to discharge said capacitor through said resistor than the time required to discharge the capacitor through the resistor in the control electrode circuit of said first-named discharge device; and each or said electric discharge devices being of such characteristics that when acurrent passage is started therethrough a subsequent energizing of the control electrode will not affect such-passage.

5. In a time delay control device for control ling the passage of a current through a load for a precisely controllable period of time, and including a. plurality of electric discharge devices each having an anode, a cathode and a control electrode, the combination comprising: a source of alternating potential; a circuit energized therefrom including a first-electric dischar e device and a first resistance in series; an independently energized circuit, including a switch, connected to the control electrode in said first electric discharge device; a second circuit including a second resistance and a second electric discharge device in series and means connecting same to said source, the first and second electric discharge devices being connected to said source in the same polarity but said first resistance beingin the cathode circuit of said first electric discharge device and said second resistance being in the anode circuit of said second electric discharge device; a circuit including a 8 capacitor and a resistor in parallel connecting the'control electrode of said second electric discharge device to the cathode of said first electric discharge device; a third electric discharge device and means connecting same and said load in series with each other and with said source; said load being in the anode circuit of said third electric discharge device and said third electric discharge device being connected to said source v in opposite polarity to that of said first and second electric discharge device; means connecting the control electrode of said third electric discharge device to the anode of said second electric discharge device; and each of said electric discharge devices being of such characteristics that when a current passage is started therethrough a subsequent energizing of the control electrode will not affect such passage.

6. In a time delay control device including a plurality of electric discharge devices each having an anode, a cathode and a control electrode, the combination comprising: a source of alternating potential; a circuit energized therefrom including a firstelectric discharge device and a first resistance in series; an independently energized circuit, including a switch, connected to the control electrode in said first electric discharge device; a second circuit including a second resistance and a second electric discharge device in series and means connecting same to said source, the first and second electric discharge devices being connected to said source in the same polarity but said first resistance being in the cathode'circuit of said first electric discharge device and said second resistance being in the anode circuit of said second electric discharge device; and a circuit including a capacitor and a resistor in parallel connecting the control electrode of said second electric discharge device to the cathode of said first electric discharge device and the first of said electric discharge devices being of such characteristics that when a current passage is started therethrough a subsequent energizing of the control electrode will not affect such passage. Y STUART C. ROCKAFELLOW.

REFERENCES CITED Name Date Schneider Mar. 1, 1949 Number 

